Tom
I think you should have replied as a boat salesman in the area.
The comercial aspect is important and, as things stand, you wuld have to advise a potential buyer of a 12m + boat that their children couldn't fish for mackerel from it within 6 miles. You could go further and ask if the children were to sit in the tender, but the tender was attached by a line to the boat, would this be alright?
These are not things for the courts to decide - the law makers should clarify.....
D